Motor drives are electric power conversion systems that convert input power from a line-side source to a different form to provide controlled drive currents to the windings of a load, such as an electric motor. Current source converter (CSC) type drives, for example, typically include a switching rectifier with AC input power being selectively switched to create a DC link current that is fed to an output inverter which creates single or multi-phase AC output current for driving a motor load at a controlled speed and torque. Both the AC to DC and DC to AC portions of the motor drive often use solid state switching components.
One difficulty in transformerless voltage source and current source inverters (VSI/CSI) is common mode output voltage between the motor load and ground, which can lead to increased stress on the motor. Common mode currents and voltages can also stress drive system components, such as internal link chokes or other components. In some instances, the peak common-mode voltage can equal the peak line-to-neutral output voltage during bus transient conditions, which can double the line-to-ground voltage on the motor. Accordingly, there is a need for an improved systems and method for reducing common mode voltage stresses in motor drives, especially during bus transients in the drive system, for example, to prevent component failures or premature degradation.